Linear Compressor

ABSTRACT

A linear compressor comprising a pump chamber wherein a moves reciprocatingly, a frame which is integral with the pump chamber and against which a floating body is reciprocatingly maintained by at least one spring, at least one electromagnet mounted on the frame for causing the reciprocating movement of the floating body. A translation rod is connected to the piston through a first articulation and to the floating body through a second articulation.

This invention relates to a linear compressor, particularly a linear compressor which is suitable for compressing refrigerant in a refrigerating device.

U.S. Pat. No. 6,641,377 B2 discloses a linear compressor with a pumping chamber in which a piston moves reciprocatingly, a frame fixedly connected to the pumping chamber, on which an oscillating body can be moved reciprocatingly by means of at least one spring, an electromagnet mounted on the frame for driving the reciprocating movement of the oscillating body, and a piston rod which connects the oscillating body to the piston.

The spring is a diaphragm spring whose edge is fastened to the frame annularly surrounding the pumping chamber, and to whose centre the beaker-shaped oscillating body and one end of the piston rod are screwed. The other end of the piston rod is spherical and engages in a cup formed on the piston so that the piston rod and the piston are able to move pivotably relative to each other. The pivotable movement prevents the transmission of torques from the oscillating body via the piston rod to the piston, which could cause the piston to move in a tilting, difficult fashion in the pumping chamber. To provide sufficient protection against tilting the piston must of a considerable length. A great deal of space is therefore required in the pumping chamber for the piston so that the ratio of the pumping chamber volume to the throughput is rather unfavourable.

However, the piston rod may also transmit to the piston forces that are orientated transversely to the direction of movement of the piston in the pumping chamber, which forces press the piston against a lateral wall of the pumping chamber. A grinding contact between the piston and the lateral wall would result in considerable frictional wear, so that in the said publication it is proposed to provide an air bearing to prevent such contact between the lateral wall and the piston by causing compressed gas to be branched off from the high pressure side of the linear compressor and to be guided through openings in the lateral wall into the pumping chamber. The gas film formed here along the lateral wall prevents direct contact between the pumping chamber wall and the piston provided that the gas throughput is sufficiently high.

The greater are the transverse forces that the piston rod is able to exert on the piston the more gas must be returned to prevent contact between the piston and the wall. This reduces the efficiency of the compressor.

The object of the invention is to provide a linear compressor in which the transmission of transverse forces from the oscillating body to the piston is minimised.

The object is achieved in that the connection of a translation rod articulated to the piston to the oscillating body is formed by a second joint. The translation rod is therefore only able to transmit essentially tensile and shearing forces to the piston, but no appreciable lateral forces.

The two joints may be formed particularly easily and inexpensively by an elastically flexible rod.

This rod is preferably designed integrally with the translation rod and thinner than the latter in order to achieve the required degree of flexibility.

The first joint preferably connects the translation rod to a piston rod anchored rigidly on the piston and guided in the pumping chamber.

Further features and advantages of the invention are apparent from the following description of an exemplary embodiment with reference to the attached figures, where:

FIG. 1 shows a perspective view of a linear compressor according to the invention;

FIG. 2 shows, in detail, the translation rod, the pumping chamber and part of the oscillating body in an ideal alignment; and

FIGS. 3 and 4 each show, on an analogy with FIG. 2, two practically relevant cases of a non-ideal alignment of the piston and oscillating body.

The linear compressor shown in FIG. 1 in a perspective view has a rigid frame that is approximately U-shaped in elevation and that is composed of three parts, namely two flat wall sections 1 and one arc 2. A first diaphragm spring 3 is clamped between narrow sides of arc 2 and of the two wall sections 1 facing each other; a second diaphragm spring 4 of the same design as diaphragm spring 3 is fastened to the narrow sides of wall sections 1 facing away from the arc. Diaphragm springs 3, 4 punched out of spring sheet steel each have an elongated edge strip which covers the narrow sides of wall sections 1, and four spring limbs 5 which extend in zigzag fashion from the ends of the edge strips to a central section 6, on which they converge. Central section 6 has three bores, two outer bores on which a permanently magnetic oscillating body 8 is suspended by means of screws or rivets 7, and a central bore through which, at diaphragm spring 3, extends a rod section 10 fastened to oscillating body 8, e.g. by means of a screw connection. Rod section 10 is connected to a translation rod 9 formed in this case from spring steel by means of a flexible tapered section 11. A second tapered section 12 connects translation rod 11 integrally to a piston rod 13, which engages in a pumping chamber 14 supported by arc 2, is guided through a bore in an end wall of the pumping chamber and is connected in pumping chamber 14 to a piston 15 that is movable therein (see FIG. 2).

Two electromagnets with an E-shaped yoke and a coil wound round the central leg of the E are each arranged between oscillating body 8 and wall sections 1 with pole shoes facing the oscillating body, and serve to drive an oscillating movement of oscillating body 8.

Since piston rod 13, rigidly connected to piston 15, is guided in the end face bore of pumping chamber 14, piston 15 is protected against tilting, even when its extension in the direction of the reciprocating movement is small. Piston 15 therefore occupies little space in pumping chamber 14, so that a large effective volume is obtained with small external dimensions.

Pumping chamber 14 is surrounded annularly by a cavity 16, which communicates with pumping chamber 14 by a multiplicity of openings 17 in its lateral wall, and which is fed through a passage 18 with compressed gas branched from a pressure connection 19 of the pumping chamber. The compressed gas penetrating pumping chamber 14 through openings 17 forms on the lateral wall a cushion on which piston 15 slides essentially free of friction.

In the ideal case translation rod 9, as shown in FIG. 2, extends rectilinearly between oscillating body 8 and piston 15, and the directions of movement of oscillating body 8 and piston 15 are exactly parallel. In practice deviations from such an ideal configuration always occur due to production tolerances, whether this is because pumping chamber 14 does not lie exactly flush with oscillating body 8 or whether it is because the direction of movement of oscillating body 8 does not coincide with that of piston 15 due to tolerances in fastening diaphragm spring 3, 4 to the frame and oscillating body 8.

FIG. 3 shows, in a representation similar to FIG. 2, the case of a lateral displacement between oscillating body 8 and piston 15. The longitudinal axes of head section 10 and piston rod 13 are parallel, but not collinear. The deviation is absorbed by a slight elastic displacement of tapered sections 11, 12 and a slight oblique position of translation rod 9. Piston 15 runs reciprocatingly in pumping chamber 14 without appreciable tilting torques or lateral forces acting on it to press piston 15 against a wall of pumping chamber 14. The clearance between piston 15 and the pumping chamber wall may therefore be kept small so that only a small gas throughput is required for supporting piston 15 and a correspondingly high efficiency of the compressor can be achieved.

FIG. 4 shows the case of an alignment of the directions of movement of oscillating body 8 and piston 15 that are not exactly parallel. This can be compensated for by means of flexible tapered sections 11, 12, the translation rod 9, represented by dotted lines, performing not only a displacement but also a slight rotation between the points of reversal of its movement.

In principle tapered sections 11, 12 could also be replaced by ball and socket or cardan joints. However, the construction with tapered sections can be produced suitably and economically, particularly for miniaturisation. 

1-7. (canceled)
 8. A linear compressor comprising: a pumping chamber in which a piston moves reciprocatingly; a frame fixedly connected to the pumping chamber; an oscillating body being retained on the frame by means of at least one spring so that the oscillating body moves reciprocatingly; at least one electromagnet mounted on the frame for driving the reciprocating movement of the oscillating body; and a translation rod connected to the piston with a first joint and connected to the oscillating body by a second joint.
 9. The linear compressor according to claim 8, wherein the first and second joints each have two degrees of pivoting freedom.
 10. The linear compressor according to claim 8, wherein at least one of the first and the second joint is formed from an elastically flexible rod.
 11. The linear compressor according to claim 10, wherein the rod is formed integrally with the translation rod and is thinner than the translation rod.
 12. The linear compressor according to claim 11, wherein the translation rod is formed from spring material.
 13. The linear compressor according to claim 8, wherein the piston is pressure gas mounted in the pumping chamber.
 14. The linear compressor according to claim 8, wherein the translation rod is connected by the first joint to a piston rod rigidly mounted on the piston and guided in the pumping chamber. 